CuZn39Pb3铅黄铜接头螺纹处在进行密封测试时发生开裂。通过宏观观察、扫描电镜分析、金相检验、能谱分析等方法对接头开裂的原因进行了分析。结果表明：铅黄铜接头显微组织中大量铅聚集于晶界，弱化了晶界强度，降低了材料的抗拉强度和塑性，当机加工残余应力和装配应力超过螺纹处部分晶界的耐受极限时，螺纹处产生微裂纹，微裂纹连接扩展最终导致铅黄铜接头开裂。

The thread of CuZn39Pb3 lead brass joint cracked during the sealing test. The causes of joint cracking were analyzed by means of macroscopic observation, scanning electron microscope analysis, metallographic examination and energy spectrum analysis. The results show that a large amount of lead concentrated in the grain boundary, weakening the grain boundary strength and reducing the tensile strength and plasticity of the material. When the machining residual stress and assembly stress exceeded the tolerance limit of part of the grain boundary of the thread, microcracks would appear at the thread, and the microcracks would eventually lead to the cracking of the lead brass joint.